Timer Motor Driven

Discussion in 'General Electronics Chat' started by mesamune80, Apr 22, 2009.

  1. mesamune80

    Thread Starter New Member

    Jun 26, 2007
    4
    0
    Hi all,

    I am having a very weird problem form my motor timing circuit,ok now i'll explain my problem:

    1) when SW is push and release (trigger oin 2 of 555 Timer),the IC start its count (set it to be 5 minutes time)...but after about 3 minutes when the pedal is press then my timer got stopped.But if you let the time elapse without pressing the pedal from the start then the time will count to 5 minutes.

    2)The motor seem to loss power (slow down) if compare to direct power up form 6V cell (6V 4.5Ah/20HR)

    is there any method to boost my output current to my motor from the 555 timer ? or any circuit modification i can make to acheive this?

    i am uisng the timer to control my time for my motor,i want it to be after 5 minutes my motor power will be cut off after trigger the SW.
    Here i attached my circuit,please take a look. thanks .
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    There is no back emf diode fitted across the motor so commutation of the motor will generate high electrical spikes and affects the operation of the 555. If the pedal is not pushed, the motor is not ON so no interference.

    You are using a Darlington transistor to drive the motor. What you doesn't know is that there could be about 1.5~2V drop across the C-E pin of the transistor, meaning the motor only getting 4.5V or less. So this is a bad idea.

    The easiest way is to use a MOSFET instead to drive the motor because if used properly, there is only about 0.5V or less across it so the motor gets 5.5V and operation of the motor is not affected. Given you have only about 5V drive available from the output of the 555, you will need to use a "Logic Level" MOSFET.
     
  3. mesamune80

    Thread Starter New Member

    Jun 26, 2007
    4
    0
    :) thanks for the idea and suggestion.So what i need to modify in my circuit is the position of my diode (should across my motor instead of transistor).
    and MOSFET......should i use IRF540N ? is it a "Logic Level" MOSFET?
    And one more think is the diode i am uisng should i change it to schottky?
    How do i know which schottky is suitable for my circuit?
     
  4. mesamune80

    Thread Starter New Member

    Jun 26, 2007
    4
    0
    ok...so the L is stand for Logic Level Type.
    ok i'll add a capacitor form pin 8 of 555 but can i use 100nF instead of 10nF?
    Thanks.
     
  5. tkng211

    Well-Known Member

    Jan 4, 2008
    65
    2
    Another suggestion for using 2 transistors to replace the logic level MOSFET in case you can hardly get it or it's relatively expensive. The specification of the first transistor is Ic max.>500mA, HFE>150; the motor driving transistor is Ic max>5A, HFE @ saturation>20.
     
  6. mesamune80

    Thread Starter New Member

    Jun 26, 2007
    4
    0
    So the 1st transistor i choosed P2N2222A Icmax = 600mA bipolar transistor and the second one i use BUL45 Bipolar transistor its Icmax = 5A is it ok? Can i change the diode across the motor to 1N4006?
    how to size the 18R resistor ? why 18R? 3W? can you explain abit thanks
     
    Last edited: Apr 22, 2009
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